Automatic test systems for testing printed circuit boards utilize a multitude of points on the printed circuit board to which are applied various stimulus signals. Simultaneously with the application of these stimulus signals, other points on the printed circuit board are monitored for a response to the stimulus signals. By analyzing the results of the responses, it can be determined which points on the printed circuit board are connected to each other and which points are isolated. By comparing this data to the data of a reference, known good printed circuit board, or design data used to create the printed circuit board, it can be determined if the board was properly manufactured.
Typical printed circuit board test systems include large numbers of programmable signal drivers for producing the various stimulation signals to be applied to the printed circuit board under test. These systems further include a large number of programmable signal receivers for receiving the signals produced by the printed circuit board under test in response to the stimulus signals. Due to the rapid advances in surface mount technology and multi-layer fabrication techniques, many of the circuit boards require large numbers of test points or points located on the circuit board with minimal spacing such that these printed circuit boards exceed the capabilities of present automatic test systems.
Due to the greater densities and the use of surface mount technology on both sides of printed circuit boards, it has become necessary to test both sides of printed circuit boards to determine whether the board was correctly manufactured. Using present technology, in order to test both sides of a printed circuit board, a top and bottom fixture is utilized. The top fixture includes test probes that interface with the test points on the printed circuit board top surface. These test probes are interconnected to interface probes that will mate with probes on the bottom fixture which are in turn connected to an automatic test system. Therefore, for each point on the top surface of a printed circuit board that requires testing, three test probes and an interconnection are required. Top and bottom test fixturing is much more expensive than single sided testing and in low quantity production printed circuit board runs, this cost can be prohibitive.
A need has thus arisen for a printed circuit board test system to reduce the number of test points required to test a circuit board and wherein each side of a printed circuit board can be separately tested from a single sided test fixture to ensure that a complete and accurate test of a printed circuit board is achieved while reducing cost considerations.